This invention relates to hermetically seared electrical component mounting prates and enclosures. In particular, the invention is a method of creating a hermetically sealed electrical component enclosure or mounting plate having electrically conductive regions passing through the enclosure walls or the plate such that the hermetic seal will not be bleached during thermal cycling.
There has long been a need to provide hermetically sealed enclosures for electrical components in order to protect the electrical components from damaging environmental conditions such as moisture and airborne dust. Electrical components and electrical circuits mounted in hermetically sealed enclosures are often used in equipment which is subjected to wide temperature and pressure variations. For instance, when electrical components are used on an aircraft which rises from ground level into the upper atmosphere the temperature can drop more than a hundred degrees fahrenheit. These temperature variations, particularly when repeated, often create problems with the seal between electrically conductive regions in the electrical component enclosures as discussed below.
The most common method of creating electrically conductive regions in a sealed electrical component enclosure is to cut apertures in one or more of the enclosure walls and fill the apertures with an electrically conductive metal. This method has a severe limitation because the electrically conductive metal generally has a coefficient of thermal expansion (CTE) greater than the CTE of the enclosure material. When the ambient temperature changes from one temperature to a lower temperature, the electrically conductive metal will contract more than the surrounding wall material and will tend to pull away from the walls creating a breach. When the ambient temperature changes from one temperature to a higher temperature, the electrically conductive metal will expand more than the wall material and will tend to cause the walls to crack. In each of these situations, the hermetic seal which exists between the electrically conductive region and the surrounding walls is often breached, particularly with repetition.
The prior art discloses several methods of creating an electrically conductive region in an electrical component mounting material which does not require the use of an aperture filled with a conductive metal. One method is to use a typical semiconductor substrate material and highly dope portions of material such that electrically conductive regions are created in the material. Another method is known as thermal gradient zone melting as disclosed in U.S. Pat. No. 4,170,490 to Anthony, et al.
Each of these methods are difficult to accomplish and generally results in a high failure rate. Consequently, for each of these methods the cost of production is relatively high.
It is accordingly an object of the present invention to obviate many of the problems of the prior art and to provide a novel low cost hermetically sealed mounting plate or electrical component enclosure which can withstand thermal cycling without breach of the hermetic seal.
It is another object of the present invention to provide a novel and reliable method creating electrically conductive regions in insulative materials.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.